Discontinuous reception (DRX) is a power saving technique that can be used by a user equipment (UE) in a wireless telecommunication system. A UE that implements DRX periodically enters a sleep state or off-period by powering down much of its circuitry for a period of time. The UE then wakes up for a brief period of time to listen for control signaling from the network. The timing of the sleep and wake cycles may be coordinated with the network so that the UE is awake when the network has downlink signaling to send to the UE. Any data in the downlink direction for a UE in connected mode DRX will be delayed until the next DRX waking occasion or on-period, which is the network's next chance to contact the UE. A conventional DRX cycle comprises no signal reception activity between on-periods, as the intention is to allow the UE to power off its baseband for as long as possible. Any communication in the off-period compromises the power saving goal.
When the UE has data to transmit on the uplink, there are at least two possible DRX configurations, known as data-scheduled DRX and inactivity-based DRX. Data-scheduled DRX may be referred to as semi-persistent scheduling in Long-Term Evolution (LTE) and may be referred to as HS-SCCH-less (High-Speed Shared Control Channel-less) scheduling in Universal Mobile Telecommunications System (UMTS).
In data-scheduled DRX, the length of time between waking occasions, known as the DRX period or DRX cycle, is relatively short. The UE wakes at regularly scheduled intervals, and a data packet is transmitted in one direction or both in each on-period. That is, the UE waits for the next DRX occasion and transmits on an already scheduled grant of resources. The configuration of on-periods and off-periods persists until being switched off or modified by the network.
In inactivity-based DRX, a UE may enter a DRX off-period due to a low level of activity on the UE. The DRX period is relatively long and can become longer based on an inactivity timer. That is, the UE may go “deeper asleep” for a longer period of inactivity. When a DRX off-period has occurred because of low activity, the UE may request an uplink grant immediately upon coming out of its off-period. Any data transmission in either direction cancels the DRX configuration and the UE wakes up.
Selection of these configurations is semi-static and controlled by the network. In either configuration, the durations of the on-periods and off-periods may also be controlled by the network, and thus the term “configuration” in this context may refer to the use of either data-scheduled DRX or inactivity-based DRX as well as the use of specified on-period durations and off-period durations.
In addition to DRX, discontinuous transmission (DTX) is also possible, and DRX and/or DTX may be referred to more generically as a discontinuous communication mode. Thus, when a UE is referred to herein as being in DRX, it should be understood that the UE is in a discontinuous communication mode. Similarly, when a DRX period, DRX cycle, DRX on-period, or DRX off-period is referred to herein, it should be understood that a period, cycle, on-period, or off-period of a discontinuous communication mode is being referred to. Other references to DRX should be understood similarly.